Good question! You might check local facebook fish/pond groups rather than marketplace. There are many out there, and us fish nerds tend to be glad to take in some fish who need a new home. Some people have enormous ponds that can handle that kind of biomass without much trouble.
Another avenue could be talking to local fish stores. They will take them as a donation and sell them for you, or in some cases even buy them from you. Since they're common goldfish it's more likely they'd take them as a donation. But yeah, many pet stores are cool with taking on fish you can't home properly anymore.
If you had a few months to move, I'm pretty sure you could find takers before you moved. I sell aquarium plants as a side business and I actually hear from people starting ponds quite frequently (they're hoping they can grow tropical plants), so it's not uncommon. I suspect these kinds of people would love to take at least some of your fish.
Another avenue could be talking to local fish stores. They will take them as a donation and sell them for you, or in some cases even buy them from you. Since they're common goldfish it's more likely they'd take them as a donation. But yeah, many pet stores are cool with taking on fish you can't home properly anymore.
If you had a few months to move, I'm pretty sure you could find takers before you moved. I sell aquarium plants as a side business and I actually hear from people starting ponds quite frequently (they're hoping they can grow tropical plants), so it's not uncommon. I suspect these kinds of people would love to take at least some of your fish.